DFT Theoretical Study of 5-(4-R-Phenyl)-1H-tetrazole (R = H; OCH3; CH3; Cl) as Corrosion Inhibitors for Mild Steel in Hydrochloric Acid

Quantum chemical study, based on DFT methods at B3LYP/6-31G ( d , p ) level of theory, of four tetrazole compounds, denoted Ph-T, Me-Ph-T, MeO-Ph-T, Cl-Ph-T and reported as corrosion inhibitors in acidic medium, has been investigated in an attempt to find relationships between their molecular electronic properties and their corresponding experimental corrosion inhibition efficiencies. The global reactivity descriptors, such as the frontier molecular orbital energies ( E HOMO and E LUMO ), energy gap ∆E , electronegativity χ, absolute hardness η and softens σ, fraction of electrons transferred ∆N as well as local selectivity parameters such as Natural Atomic Populations and Fukui indices were also calculated and discussed. The calculations were undertaken in both gaseous and aqueous states for a better approach of the experimental conditions. The results showed that Cl-Ph-T presented the lowest E LUMO and the highest χ indicating its high electron acceptor ability, which can explain its good corrosion inhibition efficiency when compared to the three-other studied tetrazole derivatives. Graphic Abstract